It has been the practice in the past to test glass containers whose particular intended service is for marketing of soft drinks and beer, where the product is under pressure, by inspecting these containers optically for checks, both in the finish and in the heel. It has also been suggested to check the sidewall of the container for variations in the thickness of the wall circumferentially about the container and at several selected vertical positions of the container. The presence of a check might result in a structural failure in the container when filled with a product under pressure. The sidewalls of the containers have, by and large, been inspected only by visual observation by selectors observing the containers as they move in succession past a diffuse light source. The selectors are capable of selecting out those containers which have gross defects and in some instances will be able to segregate containers having other, more obvious, defects such as checks, seeds and blisters. It has also been proposed in the past to check the structural strength of containers by subjecting them to an internal pressure test or, as is commonly known, a "bursting strength test." The "bursting strength test," however, normally is a test conducted on statistical samples of containers, and the samples are stressed by internal pressure to the point of failure. As would be expected, this type of test has not lent itself to being a high-speed production-type test where every container would be subjected to a specific internal pressure.
Applicants have found that by subjecting containers to a radial loading on the sidewall, that those containers which have structural defects in the walls thereof or have insufficient strength to withstand a specific load, will be broken and thus effectively selected out of a line of ware being produced. The external stressing of the container is found to be a fairly acceptable substitute for impact testing containers.